Differences between assigning attribute, style, and class in div

Question

I am wondering what is the difference between two following:

 

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Answer 1

There are lot of pros and cons in both these approaches depending on the element and condition it should load/render. I don't think all of them can be explained in a single answer without giving various references in it.

You can find such answers in the following questions:

What's the difference between HTML's and CSS's width attribute?

What's the difference between the HTML width / height attribute and the CSS width / height property on the img element?